Intraocular pressure is maintained by the circulation, within the eye, of a watery substance known as the aqueous humor. The aqueous humor is formed by the ciliary processes and passes through the pupil into the anterior chamber of the eye and out of the eye via the trabeculum Canal of Schelemm. The vitreous humor-thinly gelatinous and demonstrating very low metabolism-fills the posterior segment comprising the majority of the eye's volume.
Glaucoma is the name applied to a group of diseases characterized by an increase in the intraocular pressure of the eye, which cause atrophy of the optic nerve with resultant gradual loss of vision and, if untreated, eventual blindness. The elevation of the intraocular pressure is caused by an inability to eliminate, at an adequate rate, the aqueous humor formed by the ciliary processes of the eye. As the pressure within the eye rises, the blood supply to the optic nerve is hindered and vision is reduced. Resultant damage to the optic nerve is irreversible.
Glaucoma can often be controlled by medication that increases the drainage of the aqueous humor, such as the para-sympathetomimetics, or by medication that reduces the inflow of aqueous humor, such as the carbonic anhydrase inhibitors or the sympathetomimetics. If the administration of medication fails to control the intraocular pressure, it becomes necessary surgically to create an artifical drainage system using the patient's own tissue. This is accomplished by creating a hole in the sclera through which the aqueous humor can drain into the subconjunctival space.
Artificial implant devices comprising, either a drainage tube or a needle, and valve means, have heretofore been inserted into the anterior chamber of the eye to drain the intraocular fluid into the extraocular space beneath Tenon's capsule, in an attempt to relieve elevation of intraocular pressure. Several articles in the medical literature have disclosed artificial implant devices for the drainage of intraocular fluid. See, Peyman, et al., "An Experimental `Aqueous Shunt` for the Regulation of Intraocular Pressure," Canadian Journal of Ophthalmology Vol. 9, 463-67 (October 1974) (disclosing an artificial valve for draining the anterior chamber of the eye into the subconjunctival space); Krupin, et al., "Value Implants in Filtering Surgery", American Journal of Ophthalmology, Vol. 81, No. 2, 232-35 (February 1976) (disclosing an artificial valve implant connecting the anterior chamber of the eye to an intrascleral pocket); and Krupin, et al., "Filtering Value Implant Surgery For Eyes with Neovascular Glaucoma," American Journal of Ophthalmology, Vol. 89, No. 3, 338-43 (March 1980). (diclosing the use of their artificial implant in treating neovascular glaucoma).
Prior art artificial valve implants such as described in the above-noted literature have generally comprised valves seated in tubular housings connected to hollow needles of generally circular cross section. The tube of the needle is generally either linear or curved with radii to fit the shape of the eye, and designed for insertion of the needle portion into the anterior chamber of the eye. The curved generally circular cross section hollow needles of the prior art artificial valve implants better conform those implants for placement in a plane parallel to and in closer proximity with the plane of the ocular surface formed by the lens and the iris.
The presently used, prior art ophthalmic valve implant devices generally have been designed and constructed for insertion into the anterior chamber, necessarily requiring correspondingly fine valves and fine hollow needles. Presently used ophthalmic valve implant devices, because of their restricted use in draining the anterior chamber, drain the aqueous humor to the limbus. Drainage of the aqueous humor to the limbus is usually undesirable because the limbus is frequently scarred from previous medication or surgery, and/or may be inflamed, making drainage difficult. The anterior chamber itself is a small space between the iris and the cornea. The anterior chamber can be extremely shallow or even absent, making placement of the needle difficult or impossible. Consequently, the hollow needle often comes in contact with the iris or the cornea so that the lumen of the needle can become plugged. If a surgeon attempts to insert the hollow needle of the known valve implant devices at other anatomical sites in the eye by bending the needle, the lumen of the needle can become kinked and occluded, therefore hindering or preventing drainage of the aqueous humor through the valve implant device.
Presently available valve implant devices also generally require an extra surgical step of first piercing the eye before insertion of the valve implant.
Ophthalmic valve implant devices incorporating double reed type valves in their design are also known and are currently used. A particular disadvantage of these valves is the imprecise and relatively difficult regulation of the opening pressure of the valve.
Existing valve implant devices of unitary construction which may be implanted into the posterior chamber exhibit numerous problems. Material choice may be limited since one material has to function as a valve and stem portion requiring flexibility (for the valve) and rigidity (for the stem) simultaneously. Barbs, anchoring sutures or other fastening means existing in prior art implant valves are also necessary to secure the implant valves to the eye. Existing valve implant devices also only drain fluid to surrounding anatomical structures through a single channel. If the single channel becomes occluded drainage can be severely impeded or stopped altogether.
The critical lack in the art of ophthalmic surgical valve implant apparatus specifically designed for insertion in and drainage of the posterior chamber of the eye is apparent. As a result, there is a need in the art for an ophthalmic surgical valve implant apparatus which is specifically designed for use in draining the posterior chamber or segment of an eye afflicted with glaucoma. The optimal anatomical site for drainage when the limbus is scarred or inflamed is the posterior segment or chamber of the eye. Surgical creation of a hole in the sclera with the patient's own tissue through which the aqueous humor can drain into the subconjunctival space is far less desirable than using an ophthalmic surgical valve implant affording insertion into the posterior segment or chamber of the dye, which would further obviate drainage to a scarred, surgically altered or inflamed limbus.
Insertion into the posterior segment or chamber of the eye of an ophthalmic surgical valve implant apparatus better conforming to the natural curvature of the eye would obviate the need to anchor the implanted valve using sutures, barbs or other fastening means, since the conforming shape would be less likely to work loose after implanting. Furthermore, a valve implant of distinct and separate elemental construction, rather than unitary construction, eliminates some of the afore-noted material problems associated with the known unitary microfine valves.
The art also lacks an ophthalmic surgical valve implant apparatus capable of drainage through an array of discharge perforations, which would minimize the occluding of a single drainage channel. Also lacking in the art is a self-piercing ophthalmic valve implant device that eliminates the first surgical step of separately piercing the eye before insertion. Finally, easier and more precise regulation of valve opening pressure is needed than can be accompished using the known double reed type valves.